Inherent potassium-induced synergy and transformation during steam co-gasification of Giant Miscanthus with Napier grass biochar

In this study, the possibility of obtaining a catalytic effect from the co-thermal processing of Napier Grass (NG) biochar with raw Giant Miscanthus (GM) was investigated. The NG whole plant (NGC), NG stem part (NGSC), and demineralized NG (DNGC) were used to prepare various biochar samples under four temperatures (NGC300, NGC400, NGC500, and NGC600), and then the steam co-gasification of NG-biochar and GM was performed. It is found that a higher gasification temperature and a higher biochar blending ratio resulted in higher synergy effect in syngas production, and in the best mixing ratio (1:2 biomass to biochar), a maximum of 110 mmol/g (daf) gas yield was achieved by combining GM and NGC500 at a temperature of 850 degrees C and a steam flow rate of 0.1 g/min while there was a 28 mmol/g-biomass (daf) yield with GM only. Here, we explored the relationship between biochar characterization and co-gasification performance by considering the transformation behavior of inherent K in NG biochar as a catalytic species. XRD analysis showed that crystallized K forms (KCl mainly) in biochar could be transformed into more fixed forms like KAlSi3O8, K2SiO3 and K2SO4 after the co-gasification process while the majority was volatilized. Based on the catalytic index (CI) of biochar, it is confirmed that the effect of K in NG-biochar is more prominent than those of other alkali metals like Na, Ca, and Fe.